Conductive nanostructures, owing to their submicron dimensions, are capable of forming thin conductive films. Often the thin conductive films are optically transparent, also referred to as “transparent conductors.” Copending and co-owned U.S. patent application Ser. Nos. 11/504,822, 11/871,767, and 11/871,721 describe transparent conductors formed by interconnecting anisotropic conductive nanostructures such as metal nanowires. Nanostructure-based transparent conductors are particularly useful as transparent electrodes such as those coupled to thin film transistors in electrochromic displays, including flat panel displays and touch screens. In addition, nanostructure-based transparent conductors are also suitable as coatings on color filters and polarizers, and so forth. The above co-pending applications are incorporated herein by reference in their entireties.
To prepare a conductive film or a nanostructure network layer, a liquid dispersion of the nanostructures can be deposited on a substrate, followed by a drying or curing process. The liquid dispersion is also referred to as an “ink composition” or “ink formulation.” The ink composition typically comprises nanostructures (e.g., metal nanowires) and a liquid carrier (or dispersant). Optional agents, such as a binder, a viscosity modifier, and/or surfactants, may also be present to facilitate dispersion of the nanostructures and/or immobilization of the nanostructures on the substrate.
A thin film of a nanostructure network layer is formed following the ink deposition and after the dispersant is at least partially dried or evaporated. The nanostructure network layer thus comprises nanostructures that are randomly distributed and interconnect with one another and with the other non-volatile components of the ink composition, including, for example, the binder, viscosity modifier and surfactant.
As disclosed in co-owned U.S. patent application Ser. No. 11/504,822 cited above, roll-to-roll web coating is compatible with such solution-based deposition (coating) processes for transparent conductor fabrication. In particular, web-coating produces substantially uniform and reproducible conductive films on flexible substrates (“web”). Suitable roll-to-roll deposition processes can include, but are not limited to, slot die, gravure, reverse gravure, micro-gravure, reverse roll and Mayer-bar. There is a need to further enhance the uniformity and reproducibility of conductive films.